The purpose of this study is to examine the structural relationships among depression, parenting stress, and smart media overdependence in mothers of young children, and to verify the mediating effect of parenting stress within this framework. Data from 1,489 mothers aged from their teens to their fifties were obtained from the second wave (2023) of the Korean Early Childhood Education and Care Panel Study (K-ECEC-P), and the data were analyzed using structural equation modeling with SPSS 27.0 and AMOS 27.0. The main findings are as follows. First, maternal depression had a significant positive effect on parenting stress (β = .86, t = 20.37, p < .001). Second, parenting stress had a significant positive effect on smart media overdependence (β = .32, t = 8.71, p < .001). Third, parenting stress had a significant positive mediating effect between depression and smart media overdependence (ab = .28, p =.000). These findings indicate that maternal depression increases parenting stress, which in turn elevates the risk of smart media overdependence, and that parenting stress plays a mediating role in this relationship. The results of this study provide foundational evidence for the development of family- and society- level support strategies aimed at reducing maternal depression and parenting stress, and are expected to contribute to addressing smart media overdependence among mothers of young children.